Which of the following is not a property of a transaction?
Answer: B
Correct answer: Simplicity
Simplicity is not a transaction property. The four are Atomicity, Consistency, Isolation and Durability - ACID - and they are guarantees the system makes, not qualities of the code.
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What is the action of tetracycline in prokaryotes?
Answer: C
Correct answer: It blocks the binding of amino-acyl tRNA to the A site of ribosomes
Tetracycline binds the 30S subunit and prevents the incoming aminoacyl-tRNA from occupying the A site, so elongation cannot proceed. It is selective because bacterial cells concentrate the drug actively while human cells do not, and because the 70S ribosome differs from our 80S one.
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When was the genetic code completed?
Answer: C
Correct answer: 1966
The genetic code was completed in 1966, all 64 codons having been assigned, chiefly through the work of Nirenberg, Khorana and Holley - who shared the 1968 Nobel Prize for it. Nirenberg’s first assignment, poly-U coding for phenylalanine, had come in 1961.
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A data warehouse administrator is concerned with which of the following?
Answer: B
Correct answer: The time to make a decision and the typical roles of a database administrator
A data warehouse administrator does everything a database administrator does - storage, backup, tuning, security - and is additionally judged on how fast the warehouse can answer a question, since its whole purpose is to support decisions. A warehouse that is correct but slow has failed at its job.
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When transaction Ti requests a data item currently held by Tj , Ti is allowed to wait only if it has a timestamp larger than that of Tj (that is, Ti is younger than Tj ). Otherwise, Tj is rolled back (Tj is wounded by Ti ). This is
Answer: C
Correct answer: Wound-wait
Wound-wait is the preemptive scheme: an older transaction requesting a resource held by a younger one wounds it - the younger is rolled back - while a younger one requesting from an older simply waits. Here waiting only ever goes from young to old, so again no cycle forms. Both schemes keep the original timestamp on restart, which prevents starvation.
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A transaction may not always complete its execution successfully. Such a transaction is termed
Answer: A
Correct answer: Aborted
A transaction that cannot complete is aborted, and everything it did is undone so that the database is left as though it had never started. It may then be restarted, or abandoned if the failure was in its own logic.
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Which of the following are characteristics of a transaction?
Answer: D
Correct answer: All of the mentioned
The ACID properties are Atomicity (all or nothing), Consistency (the database moves from one valid state to another), Isolation (concurrent transactions do not see each other’s partial work) and Durability (a committed transaction survives a crash). All three listed are among them.
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State true or false: Information residing in the volatile storage does not usually survive system crashes
Answer: A
Correct answer: True
Volatile storage - main memory and cache - loses its contents when power fails or the system crashes. That is precisely why durability requires writing to non-volatile storage: the log must reach disk before a commit can be reported, or a committed transaction could vanish.
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Execution of a transaction in isolation preserves the _________ of a database
Answer: B
Correct answer: Consistency
Isolation exists to preserve consistency: if each transaction taken alone leaves the database valid, then running them so that none sees another’s intermediate state leaves it valid too. Without isolation, two individually correct transactions can interleave to produce an incorrect result - two withdrawals both reading the same balance, for instance.
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Transaction management ensures ____________ and __________ properties.
Answer: B
Correct answer: Atomicity and Durability
Transaction management is responsible for atomicity - making a transaction all-or-nothing - and durability - making a committed transaction permanent. Both rest on the recovery system and its log. Isolation is the separate business of concurrency control.
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